1994 Fiscal Year Final Research Report Summary
Research on the Mechanism of Fatigue Damage in Composite Materials
| Project/Area Number |
04402021
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| Research Category |
Grant-in-Aid for General Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
Aerospace engineering
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| Research Institution | KYUSHU UNIVERSITY |
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Principal Investigator |
KUNOO Kazuo Kyushu University, Engineering, Professor, 工学部, 教授 (90128009)
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| Co-Investigator(Kenkyū-buntansha) |
ONO Kousei Kyushu University, Engineering, Assistant Professor, 工学部, 助手 (90038092)
UDA Nobuhide Kyushu University, Engineering, Associate Professor, 工学部, 助教授 (20160260)
SAKURAI Akira Kyushu University, Engineering, Professor, 工学部, 教授 (80037952)
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| Project Period (FY) |
1992 – 1994
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| Keywords | Composite Materials / Fatigue / Delamination / Acoustic Emission / Failure / Failure Mode / PEEK Matrix / Epoxy Matrix |
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| Research Abstract |
We developed programs of a personal computer to control a fatigue loading system. The purpose of the program is to avoid reduction of load in the progress of fatigue failure, to measure precisely the stiffness reduction ratio and to pick a replica of a specimen every specified cycle. To cope with a tab failure during a fatigue test, we conducted a finite element analysis of a specimen with a tab and proposed the new tab with urethane foam on a specimen which gave reliable experimental results. The experimental results of 45-degree angle-ply laminates subjected to tension-tension repeated load showed that the stiffneess reduction ratio of epoxy matrix was higher than that of PEEK matrix and the fatigue life of epoxy matrix was much lower than that of PEEK matrix. In the case of [<plus-minus>45]_<4s> specimen of epoxy matrix, crack density in the free-edge region and acoustic emission rate increased after 100 repeated loads. The failure mode of a quasi-isotropic laminate subjected to tension-tension repeated load depended on the difference of matrix and directions of tension load. However in the case of compression-compression repeated load, stacking sequence of a laminate did not deeply affect failure. The stiffness reduction rate versus a number of cycles became low after 30% of fatigue life and was 60% just before fatigue failure. The failure mode of epoxy matrix showed brittleness, but the failure mode of PEEK matrix showed ductility.
We developed a simplified method for determining the strain energy release rate components of free-edge delamination in composite laminates. As that was verified by a finite element analysis, it is very useful to clarify a failure mechanism of fatigue.
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